It's basically confusing "math" (which they had and like all of us were overwhelmed by how neat it is and how much you can do with "thinking rationally") with "science" which they didn't really have. "Math" is hermetic and Science is a negotiation between our representation systems and "What's out there?"

I.e. it is really difficult (didn't happen) to guess the "self-evident" principles and operations that will allow you to deduce the universe. And being super-rational without science is one of the most dangerous things humans have come up with.